1. Field of the Invention
The present invention relates to an improved cycloidal mass spectrometer which employs modified time of flight characteristics so as to provide a smaller and more efficient high-resolution magnetic mass spectrometer.
2. Description of the Prior Art
The use of mass spectrometers in determining the identity and quantity of constituent materials in a gaseous, liquid or solid specimen has long been known. It has been known, in connection with such systems, to analyze the specimen under vacuum through conversion of the molecules into an ionic form, separating the ions by their mass to charge ratio, and permitting the ions to bombard a detector. See generally U.S. Pat. Nos. 2,882,410; 3,070,951; 3,590,243; and 4,298,795. See also U.S. Pat. Nos. 4,882,485 and 4,952,802.
In general, ionizers contain an ionizer inlet assembly wherein the specimen to be analyzed is received, a high vacuum chamber which cooperates with the ionizer inlet assembly. An analyzer assembly is disposed within the high vacuum chamber and is adapted to receive ions from the ionizer. Detector means are employed in making a determination regarding the constituent components of the specimen employing mass to charge ratio as a distinguishing characteristic. By one of many known means, the molecules of a gaseous specimen contained in the ionizer may be converted into ions which are analyzed by such equipment.
It has been known with prior art cycloidal mass spectrometers to use a single collector and ramped electric field in looking at only one mass to charge ratio at a time.
In known mass spectrometer systems, whether of the cycloidal variety or not, the analyzers are quite large and, as a result, dominate the design and specifications of the systems to be employed therewith.
U.S. Pat. No. 5, 304,799 discloses an improved cycloidal mass spectrometer of reduced dimension. The disclosure of this patent is expressly incorporated herein by reference.
Time of flight magnetic mass spectrometers typically involve acceleration of ions and identification based upon the time that it takes the ions to arrive at the detector. To operate efficiently and achieve the desired resolution at higher molecular masses, the flight paths must be very long and, as a result, in respect of higher molecular masses, it is difficult to achieve the desired resolution and the equipment can be expensive. One of the challenges in such a system is the need to maintain a uniform magnetic field throughout the entire path of ion flight.
Position resolving mass spectrometers employ the effect that ions of different molecular weight move in different flight paths and make determinations based upon the portion of the detector impacted by the ions.
There remains, therefore, a very real and substantial need for an improved magnetic mass spectrometer and an associated method which can employ general principles of time of flight spectrometers and cycloidal mass spectrometers while achieving enhanced resolution in an instrument which is of relatively small size.
The present invention has met the above-described needs.
The method of separating ions according to mass employing mass spectrometry includes establishing in phase 1 a stream of ions traveling in a generally cycloidal path in an electric field and a magnetic field. The electric field is caused in phase 2 of the method to terminate while maintaining the magnetic field, thereby causing the ions to travel in a circular path within the magnetic field for a predetermined number of times, after which the electrical field is reestablished, thereby causing the ions to travel in a further cycloidal path (phase 3) and thereby to effect movement either into or not into an associated detector. Appropriate microprocessor means receives output from the detector responsive to impingement of ions thereon.
The method, therefore, combines concepts of cycloidal mass spectrometry with a much improved time of flight concept wherein circular motion within a limited region of a uniform magnetic field is employed.
The corresponding apparatus provides a cycloidal ionizer for converting a specimen into a plurality of ion beams which travel in a generally cycloidal path within a magnetic field and an electric field. A microprocessor in phase 2 terminates the cycloidal travel and converts it to generally circular ion travel by terminating the electric field for a predetermined period of time after which the electric field is reinitiated to cause further travel in a generally cycloidal path.
It is an object of the present invention to provide a mass spectrometer which employs concepts of time of flight spectrometers and cycloidal mass spectrometers in effecting improved resolution and an associated method.
It is a further object of the present invention to provide a reduced size mass spectrometer of the foregoing type which provides improved resolution and is economically advantageous.
It is a further object of the present invention to employ such a system which requires only a relatively small magnetic field, thereby enhancing performance and reducing the cost of employing the system.
It is a further object of the present invention to provide such a system which permits automated rapid analysis of ions based upon mass to charge ratios.
These and other objects of the invention will be more fully understood from the following detailed description of the invention on reference to the illustrations appended hereto.